Electricity charges collected by electric power companies from customers are generally divided into two categories, i.e., the energy charge and the demand charge. The energy charge is the charge of the total electricity consumed by the customer during a certain period of time (e.g., during a billing month), wherein the unit of the energy is charged by kWh (i.e. kilowatt-hour). With respect to the energy charge, the electric power companies usually implement time-dependent electricity price systems (i.e., setting different electricity price rates for different time intervals) and, thereby, guiding the customers to reduce the electricity consumption during the peak time interval. As to the demand charge, it is the charge collected by the electric power company according to a maximum demand of the customer during a certain period of time (e.g., during a billing month), wherein the unit of the demand is charged by kW. Different electric power companies calculate “demand” in different ways and, generally, the demand is calculated according to the average electricity consumption power during a certain time interval (e.g., 15 minutes, or longer or shorter than 15 minutes). The electric power company collects a fixed demand charge according to a contracted capacity signed with the customer in advance. The electric power company will collect an additional charge if the maximum demand of the real power consumption of the customer exceeds the contracted capacity. By setting the contracted capacity and collecting the demand charge, the electric power company can more easily control the peak load of the overall electric power system.
Although the electric power companies can control the power supply conditions and the load of the overall electric power system by collecting energy charges and demand charges, sometimes power supply remains tight. To solve this problem, many electric power companies adopt a demand response mechanism. Briefly speaking, if an electric power company predicts that a certain time interval in a certain day will be a time interval of peak demand, the electric power company takes that day as a scheduling day and that time interval of that day as a scheduling time interval. The duration of the scheduling time interval is determined by the electric power company and is not shorter than a minimum load-reduction time interval (e.g., 2 hours). The electric power company will request customers to reduce their maximum consumed power value within the scheduling time interval of the scheduling day. The electric power company calculates a customer base line according to the maximum consumed power values of the customers within the same time interval in past several days. If the maximum consumed power value within the scheduling time interval of the scheduling day is lower than the customer base line, the customer base line minus the maximum consumed power value within the scheduling time interval of the scheduling day is the load-reduction amount of the demand-response (i.e., the reduced maximum consumed power) of the customers within the scheduling time interval of the scheduling day. Thereafter, the electric power company calculates the reward of the customer according to the load-reduction amounts of the demand-response.
Some customers utilize energy storages to reduce the dependence on the power supply systems of the electric power companies, which also reduce the load of the power supply systems of the electric power companies. Currently, energy storages are usually utilized to provide only one single service (e.g., only the service for load shifting from peak hours to off-peak hours, only the service for peak load shaving, or only the service for load reduction of demand-response) because the charge and discharge capacities of the energy storages are limited, different services have different requirements, and both the power supply conditions of the power supply systems of the electric power companies and the power consumption conditions of the customers change from time to time. When providing only one single service, the energy storages are idle in many time intervals of the day.
Specifically, if an energy storage is used for load shifting from peak hours to off-peak hours (i.e., the energy storage is charged in off-peak hours where the electricity price rate is lower, and discharged in peak hours where the electricity price rate is higher) only, the energy storage stops its operation after discharging in the peak hours. If an energy storage is used for peak load shaving (i.e., the energy storage is discharged when the consumed power of the customer exceeds the contracted power) only, the energy storage operates momentarily in a day because the time intervals during which the consumed power of the customer exceeds the contracted power are usually very short. Furthermore, if an energy storage is used only for load reduction of demand-response (i.e., the energy storage is discharged within the scheduling time interval of the scheduling day), the energy storage will not operate within the non-scheduling time intervals of the scheduling day as well as the normal days.
Since the energy storages provide only one single service, they are idle in many time intervals of the day. As the energy storages cannot be fully utilized, solving various problems associated with power consumption together to obtain more benefits (i.e., considering how to reduce the energy charge, reduce the demand charge, and obtain rewards from load reduction of demand-response together) cannot be achieved. Meanwhile, the load of the power supply systems of the electric power companies in the time intervals of peak demand cannot be significantly reduced.
Accordingly, there is an urgent need for a charge and discharge control technology that can control an energy storage to provide multiple services so as to assist customers in load shifting from peak hours to off-peak hours, peak load shaving, and load reduction and addition appropriately and timely according to the demand response mechanism to obtain more benefits and reduce the overall peak load of the power supply systems of the electric power companies.